If the LC_CTYPE category of the current locale does not define a classification rule whose name matches the property string property, the function returns zero. Otherwise, it returns a nonzero value suitable for use as the second argument to a subsequent call to towctrans.

The function determines a classification rule for wide-character codes. The following pairs of calls have the same behavior in all locales (but an implementation can define additional classification rules even in the "C" locale):